In some vehicles vacuum is used to operate or assist in the operation of various devices. For example, vacuum may be used to assist a driver applying vehicle brakes, turbocharger operation, fuel vapor purging, heating and ventilation system actuation, and driveline component actuation. If the vehicle does not produce vacuum naturally, such as from the intake manifold, then a separate vacuum source is required to operate such devices.
In boosted engines where intake manifold pressures are often at pressures greater than atmospheric pressure, intake manifold vacuum may be replaced or augmented with vacuum from an evacuator. Specifically, in one approach the evacuator may include an ejector. The ejector, as used herein, is a converging, diverging nozzle assembly with three connections, a motive port connected to a pressure source above atmospheric pressure, a discharge port connected to atmospheric pressure, and a suction port connected to a device requiring vacuum. By passing pressurized air through the ejector, a low pressure region may be created within the ejector so that air can be drawn from a vacuum reservoir or may directly act on a device requiring vacuum, thereby reducing pressure within the vacuum reservoir or device requiring vacuum.
In another approach the evacuator may include an aspirator. As used herein, the aspirator is a converging, diverging nozzle assembly with three connections, a motive port connected to the intake air at atmospheric pressure, a discharge port connected to the manifold vacuum located downstream of the throttle, and a suction port connected to a device requiring vacuum. Similar to the ejector, a low pressure region may be created within the aspirator so that air can be drawn from a vacuum reservoir or may directly act on a device requiring vacuum, thereby reducing pressure within the vacuum reservoir or device requiring vacuum. There is a continuing need in the art for improved evacuators that generate increased vacuum pressure and increased suction mass flow rate while decreasing the consumption of engine air.